FREE RADICAL INTERMEDIATES THEIR POLARIZATION DURING REDOX PROCESSES OF BILE PIGMENTS

The investigation of bile pigments (bilirubin (BR), biliverdin (BV), purpurin (Pu), choletelin (Ch) etc.) by cyclic voltammetry, in-situ rapid scanning thin layer spectroelectrochemistry and ESR spectroscopy indicates that many free radical intermediates and polymers are produced during oxidation and reduction processes.

Avian magnetic compass:Its functional properties and physical basis

The avian magnetic compass was analyzed in bird species of three different orders - Passeriforms, Columbiforms and Galliforms - and in three different behavioral contexts, namely migratory orientation, homing and directional conditioning. The respective findings indicate similar functional properties： it is an inclination compass that works only within a functional window around the ambient magnetic field intensity; it tends to be lateralized in favor of the fight eye, and it is wavelength-dependent, requiring light from the short-wavelength range of the spectrum. The underlying physical mechanisms have been identified as radical pair processes, spin-chemical reactions in specialized photopigments. The iron-based receptors in the upper beak do not seem to be involved. The existence of the same type of magnetic compass in only very distantly related bird species suggests that it may have been present already in the common ancestors of all modem birds, where it evolved as an all-purpose compass mechanism for orientation within the home range [Current Zoology 56 （3）： 265-276, 2010].

ESR study of the free radical intermediates formed during the electrolytic process——III. Electrooxidation of substituted anilines

Active free radicals formed by the electrooxidation of substituted anilines RC_6H_4NH_3 (R=H, p-Br, p-Cl, p-I, p-Me, p-COOH, p-MeCO, p-NO_2, m-CO_2H, and m-Cl) are trapped by spin trap 2-methyl-2-nitroso propane (MNP). A multiple ESR signal of the solution containing electrolytic aniline and MNP is identified with the spin adduct of MNP and radical cation 1 by theore- tical simulation of observed spectrum. Furthermore, ESR spectra of para- or meta-substituted anilines give a reasonable explanation about spin adducts of MNP and the cation 2 or 3 by the same method.

Visible-light-promoted sulfonylmethylation of imidazopyridines

The visible light promoted C-H sulfonylmethylation of imidazopyridines with easily accessible bromomethyl sulfones under mild reaction conditions was described.This protocol provides an effective and practical access to sulfonylmethylated imidazopyridines with good functional group tolerance.The desired products were provided in moderate to excellent yields for 50 examples at room temperature.The method could also be an attractive strategy to install a methyl group on imidazopyridines.

Catalyst-free,direct electrochemical trifluoromethylation/cyclization of N-arylacrylamides using TfNHNHBoc as a CF_(3) source

A new electrochemical strategy for trifluoromethylation/cyclization using TfNHNHBoc as a CF_(3)source was established.This approach was realized by the direct electrolysis of Tf NHNHBoc under external oxidantfree and catalyst-free conditions,and afforded various trifluoromethylated oxindoles with good functional group compatibility and broad substrate scope.Preliminary mechanistic studies show that the reaction proceeds by a radical process.

Visible-light-initiated 4CzIPN catalyzed multi-component tandem reactions to assemble sulfonated quinoxalin-2(1H)-ones

A mild and efficient photochemical multi-component tandem reaction of quinoxalin-2(1H)-ones, alkenes and sulfinic acids is reported. This tandem reaction could be conveniently carried out at room temperature by employing 4Cz IPN as the metal-free photocatalyst and dioxygen(air) as the environmentally benign oxidant. A number of sulfonated quinoxalin-2(1H)-ones were obtained in satisfactory yields with favorable functional group tolerance. Radical trapping experiment and fluorescence quenching experiments were performed to elucidate this visible-light mediated radical reaction process.

A copper-catalyzed three-component reaction of alkenes,cycloketone oximes and DABCO·(SO_(2))_(2):Direct C(sp^(2))-H cyanoalkylsulfonylation

A copper-catalyzed three-component reaction of alkenes,cycloketone oximes and DABCO·(SO_(2))_(2) is de-veloped,which provides a convenient route for the synthesis of diverse(E)-cyanoalkylsulfonyl alkenes in moderate to good yields with excellent regio-and stereoselectivity.A broad substrate scope with ex-cellent functional group tolerance is observed.A plausible radical pathway is proposed,which involves copper-catalyzed ring-opening C–C bond cleavage of O-acyl oxime and insertion of sulfur dioxide.During the reaction process,cyanoalkyl radical and cyanoalkylsulfonyl radical are the key intermediates.

Mechanistic insight into the synergistic Cu/Pd-catalyzed carbonylation of aryl iodides using alcohols and dioxygen as the carbonyl source

Pd-catalyzed carbonylation,as an efficient synthetic approach to the installation of carbonyl groups in organic compounds,has been one of the most important research fields in the past decade.Although elegant reactions that allow highly selective carbonylations have been developed,straightforward routes with improved reaction activity and broader substrate scope remain long-term challenges for new practical applications.Here,we show a new type of synergistic Cu/Pd-catalyzed carbonylation reaction using alcohols and dioxgen as the carbonyl sources.A broad range of aryl iodides and alcohols are compatible with this protocol.The reaction is concise and practical due to the ready availability of the starting materials and the scalability of the reaction.In addition,the reaction affords lactones and lactams in an intermolecular fashion.Moreover,DFT calculations have been performed to study the detailed mechanisms.